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CollationKey.javaAPI DocJava SE 5 API6419Fri Aug 26 14:57:20 BST 2005java.text

CollationKey

public final class CollationKey extends Object implements Comparable
A CollationKey represents a String under the rules of a specific Collator object. Comparing two CollationKeys returns the relative order of the Strings they represent. Using CollationKeys to compare Strings is generally faster than using Collator.compare. Thus, when the Strings must be compared multiple times, for example when sorting a list of Strings. It's more efficient to use CollationKeys.

You can not create CollationKeys directly. Rather, generate them by calling Collator.getCollationKey. You can only compare CollationKeys generated from the same Collator object.

Generating a CollationKey for a String involves examining the entire String and converting it to series of bits that can be compared bitwise. This allows fast comparisons once the keys are generated. The cost of generating keys is recouped in faster comparisons when Strings need to be compared many times. On the other hand, the result of a comparison is often determined by the first couple of characters of each String. Collator.compare examines only as many characters as it needs which allows it to be faster when doing single comparisons.

The following example shows how CollationKeys might be used to sort a list of Strings. 

// Create an array of CollationKeys for the Strings to be sorted.
Collator myCollator = Collator.getInstance();
CollationKey[] keys = new CollationKey[3];
keys[0] = myCollator.getCollationKey("Tom");
keys[1] = myCollator.getCollationKey("Dick");
keys[2] = myCollator.getCollationKey("Harry");
sort( keys );


//...


// Inside body of sort routine, compare keys this way
if( keys[i].compareTo( keys[j] ) > 0 )
// swap keys[i] and keys[j]


//...


// Finally, when we've returned from sort.
System.out.println( keys[0].getSourceString() );
System.out.println( keys[1].getSourceString() );
System.out.println( keys[2].getSourceString() );
see
Collator
see
RuleBasedCollator
version
1.18, 05/05/04
author
Helena Shih

Fields Summary
private String
source
private String
key
Constructors Summary
CollationKey(String source, String key)
A CollationKey can only be generated by Collator objects.

        this.source = source;
        this.key = key;
Methods Summary
public intcompareTo(java.text.CollationKey target)
Compare this CollationKey to the target CollationKey. The collation rules of the Collator object which created these keys are applied. Note: CollationKeys created by different Collators can not be compared.

param
target target CollationKey
return
Returns an integer value. Value is less than zero if this is less than target, value is zero if this and target are equal and value is greater than zero if this is greater than target.
see
java.text.Collator#compare

        int result = key.compareTo(target.key);
        if (result <= Collator.LESS)
            return Collator.LESS;
        else if (result >= Collator.GREATER)
            return Collator.GREATER;
        return Collator.EQUAL;
public booleanequals(java.lang.Object target)
Compare this CollationKey and the target CollationKey for equality. The collation rules of the Collator object which created these keys are applied. Note: CollationKeys created by different Collators can not be compared.

param
target the CollationKey to compare to.
return
Returns true if two objects are equal, false otherwise.

        if (this == target) return true;
        if (target == null || !getClass().equals(target.getClass())) {
            return false;
        }
        CollationKey other = (CollationKey)target;
        return key.equals(other.key);
public java.lang.StringgetSourceString()
Returns the String that this CollationKey represents.

        return source;
public inthashCode()
Creates a hash code for this CollationKey. The hash value is calculated on the key itself, not the String from which the key was created. Thus if x and y are CollationKeys, then x.hashCode(x) == y.hashCode() if x.equals(y) is true. This allows language-sensitive comparison in a hash table. See the CollatinKey class description for an example.

return
the hash value based on the string's collation order.

        return (key.hashCode());
public byte[]toByteArray()
Converts the CollationKey to a sequence of bits. If two CollationKeys could be legitimately compared, then one could compare the byte arrays for each of those keys to obtain the same result. Byte arrays are organized most significant byte first.


        char[] src = key.toCharArray();
        byte[] dest = new byte[ 2*src.length ];
        int j = 0;
        for( int i=0; i<src.length; i++ ) {
            dest[j++] = (byte)(src[i] >>> 8);
            dest[j++] = (byte)(src[i] & 0x00ff);
        }
        return dest;